The present invention relates to sockets that electrically connects an integrated circuit with an IC board. More particularly, the present invention is directed to a test socket for testing an integrated circuit, wherein the test socket uses a Kelvin bridge/connector to improve the accuracy over standard IC board testing devices.
Integrated circuit test devices have long been used in the semiconductor industry to test and evaluate the quality of the chips taken off the manufacturing line. Signal integrity is a critical aspect of chip design and testing. To this end, it is desirable to maintain impedance through a conducting portion of a contact interconnecting the integrated circuit lead to its corresponding load board pad at a particular desired level. The effective impedance of the design is a function of a number of factors. These include width and length of conduction path, material of which the conductive structure is made, material thickness, etc.
When testing the electrical characteristics of a packaged or molded semiconductor device such as an integrated circuit (IC), it is common to utilize a specialized test socket that secures and connects the IC to the equipment that evaluates its performance, i.e. a handler and a load board. Many different test sockets have been devised for quickly and temporarily connecting integrated circuit leads of a chip to be tested to a load board of a tester. Automated test apparatus in particular use a number of such sockets. Typical socket arrangements use force brought to bear upon a contact positioned between a lead of the IC and the load board to deform a probe tip of the contact and engage a pad on the load board. Such a configuration provides for positive connection between the pins or contact pads of the device under test (“DUT”) and corresponding leads of a test apparatus. Examples of this type of connection can be found, for example, in U.S. Pat. No. 6,409,521 to Rathburn, and U.S. Pat. No. 7,737,708 to Sherry, the teachings and contents of both of which are fully incorporated herein by reference.
U.S. Pat. No. 7,918,669, the contents of which are incorporated herein by reference, is a test socket devised by the present inventor. The socket of the '669 patent uses a unique linkage to urge the connectors of the test circuit upward where it can make contact with the test equipment. This test socket was found to be very successful in ensuring good contact with the test apparatus while reducing force on the circuit itself. A component of that test socket was an elastomer element that provided a resiliency to the link, ensuring proper contact in a cost effective and reliable manner. The cylindrical elastomer keeps the contact links in place, and their resiliency acts like a spring mechanism for the links. This allows for vertical movement on the link.
Accuracy is critical to the testing operation, as mass produced chips require knowledge of the capabilities and limits of the chips. For that reason, ways to improve the accuracy of the testing is always under review. The present invention is a test socket that uses Kelvin connectors to improve the accuracy of the test, particularly in the low voltage environment of the IC chips.